1.1—Purpose of the Invention
Enormous quantities of Natural Gas, NG, have been found recently. NG is used for electricity generation, in heating (residential and industrial), in the production of chemicals and in transportation.
Despite its abundance and the variety of its uses, the NG has a backdrop: it has a very low energy concentration at ambient temperatures and pressures. The low energy concentration makes difficult to transport the NG from the production field to the processing sites or to the markets. The purposes of the system and method described in the present invention are to enable the production from NG of:                Gasoline, and/or,        A high-energy transportable liquid. This liquid will be named “Methanoleum”, to emphasize that it is transportable in the same existing transportation infrastructure used to transport petroleum.1.2—Gasoline        
Gasoline is a mixture of alkanes, which has three prominent features:                As alkanes, they have the general formula CnH2n+2, where n is the number of carbon atoms in the alkane molecule.        The gasoline mixture contains alkanes with 5≤n≤10        The gasoline alkanes are liquids at temperatures below 20 C at atmospheric pressure.        
In the description of the process, the mixture of alkanes linear or branched synthesized in the method of this patent, and having 10≤n≤5, will be called “Natural Gas Gasoline”, NGG.
The synthetic NGG is not an exact chemical replica of the components of the regular gasoline obtained from petroleum, PG. The NGG will imitate the PG in its behavior in internal combustion engines, in its transportability and its storage.
In Table 1 we find the physical properties of the substances involved in the invention (alkanes and Hydrogen). The Molecular Mass, MM, was calculated using:MM=14n+2 [dalton]  [Eq. 1]
The table includes the boiling point, b.p., only for the linear isomers. The branched isomers have lower b.p. than their correspondent linear isomer. Branched isomers appear also in the PG mixture. They can also be formed during the process described in this patent.
TABLE 1Physical Properties of Hydrogen and relevant linear alkanes.b.p. [° C.]of theStateRoll in theLinear@25° C.,MMinvention'sSubstanceFormulaIsomer101.3 kPa[dalton]processHydrogenH2−253Gas2By-product, usedin the processMethaneCH4−16216Raw MaterialEthaneC2H6−8930IntermediatePropaneC3H8−4244productButaneC4H10−0.558PentaneC5H1236Liquid72NGG mixtureHexaneC6H146986componentHeptaneC7H1698100OctaneC8H18126114NonaneC9H20151128DecaneC10H221741421.3—Methanoleum
Methanoleum is also a mixture of alkanes: Pentane and Hexane. The higher energy concentration of liquid alkanes is shown Table 2, which contains the High Value Heat of Combustion, (ΔHc), of alkanes relevant to this invention. To convert the gravimetric value (ΔHc)G, given in [MJ/Kg], into the volumetric (ΔHc)v, measured in [MJ/L], we used:(ΔHc)V [MJ/L]=(ΔHc)G [MJ/Kg]×ρg/L×10−3  [eq. 2]where ρg/L is the density of the alkane given in [g/L].
Table 2 also includes the Volumetric Energy Concentration Ratio relative to Methane, ECR, given by:
                              E          ⁢                                          ⁢          C          ⁢                                          ⁢          R                =                                            (                              Δ                ⁢                                                                  ⁢                                  H                  c                                            )                                      V              ,              Cn                                                          (                              Δ                ⁢                                                                  ⁢                                  H                  c                                            )                                      V              ,                              CH                ⁢                                                                  ⁢                4                                                                        [                  eq          .                                          ⁢          3                ]            where:
(ΔHc)V, Cn is the Heat of Combustion of the alkane with n carbons in the molecule, and
(ΔHc)V, CH4 is the Heat of Combustion of Methane
TABLE 2Heat of Combustion, (ΔHc), for relevant alkanesDensityIncluded(ΔHc)G,@ 20° C.(ΔHc)Vin theHV[g/L]HVMethanoleumFuelMJ/KgGasLiquidKJ/LECRMixtureMethane55.5360.66837.11.00Ethane51.9261.26565.71.77Propane50.4041.86794.12.53Butane49.5952.493123.63.33Pentane49.06962630717.2827.96✓Hexane48.76965932138.8866.28✓Heptane48.50868433179.5894.33Octane48.37470334006.9916.63
From Table 2 we see that liquid alkanes included in the Methanoleum, Pentane and Hexane, carry energy per unit volume higher than 800 times the energy carried by Methane.
1.4—Prior Art
Several studies on the UV photolysis of Methane and the consequent production of higher alkanes have been performed in the past. Some examples are given in table 3.
TABLE 3UV sources in previous worksEph Photon#Authors (Year)UV SourceEnergy•[eV]1A. R. Derk, H. H. Funke and J. L.RF Krypton Discharge Lamp10.64Falconer (2008).10.032Jaehong Park, Jungwoo Lee, Kijo Sim, JinFour Wave Mixing of Krypton10.2Wook Han and Whikun Yi (2008)radiation3R. Gordon, Jr. and P. Ausloos (1967)Air cooled electrodeless10.03discharge lamps with Krypton11.83or Argon11.614Bruce H, Mahan and Robert MandalMicrowave discharge lamp with10.03(1962)Krypton5M. A Gondal, Z. H. Yamani, A. Dastgeer,Third Harmonic Nd:YAG Laser3.5M. A. Ali, and A. Arfaj (2003)6C. Rozmarin, E. Arzoumanian,1 - KrF Pulsed Excimer Laser,5.00Et. Es-sebbar, A. Jolly, S. Errier, M.-C.2 - H2/He MW Discharge Lamp10.64Gazeau, Y. Benilan (2010)1.5—Innovations
Table 3 shows that in the prior investigations, the UV sources used in Methane's photolysis were: Discharge Lamps, Gas Lasers, Doped Isolator Lasers and Non-linear media Four Wave Mixing. In contrast, in the system described in this patent, the UV source is a Semiconductor LED or Laser. Semiconductor sources have the following advantages over the sources in the past investigations:                They can be produced with a specific emission line or band, thus, they have a better efficiency conversion of electricity to the desired spectral bands or lines.        They are more compact.        They do not need to be isolated from the Methane by an enclosure transparent to UV.        
Another innovation of the present patent is the Photon Energy, Eph, used to break the C—H bond of the Methane. In the earlier works, Eph>10 eV. This high energy enables the photolysis of the C—H bond by elevating an electron from the ground electronic state to the first excited electronic state. In the present patent the C—H bond is broken by increasing the distance, rC—H, between the H and the Methyl group by vibration. The energy needed by such process is the “Bond Dissociation Enthalpy”, BDE. At T=298 K, the BDE of the H3C—H bond is 104.99 (±0.07) Kcal/mol or 4.55 eV/molecule. A photon with this energy has a wavelength λdis=272.5 nm.
Another innovation of the present patent is the use of heated UV sources. This heating avoids the formation of thin polymer films that may cover the optics of the UV source and lower the UV transmittance.
Another innovation of the present patent is the use of a controlled temperature during photolytic reactions to produce desired alkanes. The gaseous reaction media is maintained at a temperature that enables the elongation reactions of short alkanes in order to convert the short alkanes into larger chains, while trapping-out the desired alkanes by condensation.
1.6—Chemical Reactions
For simplicity of the explanation, we will consider the NG, used in the process as raw material, contains mainly Methane, CH4. We will assume that all the chemical reactions and physical separation effects take place in a closed volume that contains one or several UV sources. This volume will be called “Photoreactor”.
1.6.1—Photochemical Initiation
The first reaction of the process is the initiation reaction [1] that occurs when UV photons break the C—H bond of Methane. This reaction has been very well studied for the last 40 years. At least, five different dissociation channels have been established:CH4+hv(4.47 eV)→CH3.+H.  [1]CH4+hv(5.01−6.04 eV)→CH2:+H2  [1a]CH4+hv(9.04−9.53 eV)→CH2:+2H.  [1b]CH4+hv(9.06 eV)→CH+H2+H.  [1c]CH4+hv(9.27 eV)→C+2H2  [1d]where hv represents ultra-violet photons. The energy values (in eV) given for the photons in each reaction are based on Romanzin et al. (2005). Since the photons used in the system described in the present patent have Eph=4.55 eV, only reaction [1] is a feasible path for the photolysis of Methane. This assumption will be used in the rest of the present patent.1.6.2—The Hydrogen Path
Generally, in a Methane saturated atmosphere, the radicals react with Methane to form successively higher alkanes. The general overall reaction is:nCH4→CnH2n+2+(n−1)H2  [2]
In Methane saturated atmospheres, the most probable reaction for the Hydrogen radical will be the formation of a Hydrogen molecule, while reacting with Methane:H.+CH4→CH3.+H2  [3]
To avoid the reverse reaction:CH3.+H2→H.+CH4  [3]R the H2 is filtered out from the System through a Membrane Hydrogen Filter, by Buoyancy or Centrifugally. The filtered out Hydrogen molecules are transferred to an Electricity Generator, where the H2 is oxidized by ambient Oxygen.2H2+O2→2H2O  [4]1.6.3—Reactions of the Methyl Radical with Methane
The concentration of Methyl radicals in the Photoreactor increases constantly since:                The UV Sources are active continuously and reaction [1] is taking place all the time.        All the Hydrogen radicals are converted into Methyl radicals by the propagation reaction [3].        Hydrogen molecules are extracted from the Photoreactor, so the possibility of the reverse reaction [3]R is avoided continually.        
In Methane saturated atmosphere, as the one that exists in the Photoreactor, the Methyl radical reacting with Methane molecules, has 2 probable paths:CH3.+C′H4→CH4+C′H3.  [5]CH3.+CH4→C2H6+H.  [6]
At the first look reaction [5] may be considered as a meaningless “dummy” reaction. In the absence of isotopic marking it is impossible to follow its existence. But, reaction [5] enables, in rich Methane environments, a very long “life time” to the Methyl radical and the increase of Methyl radical concentration in the Photoreactor.
Reaction [6] has a low probability to occur because of steric hindrance reasons. But, since the population of Methane is big, it may occur. The resulting H. from reaction [6] will enter into the Hydrogen path described in paragraph 1.6.2. This statement also is valid for other H. formed in reactions that will be presented in the following paragraphs.
1.6.4—Ethane Formation by Termination
Let's assume a constant irradiation of UV photons into the gas mixture. After a radiation period, Δt1, the concentration of the Methyl radical will increase at such a point that the formation of Ethane by the termination reaction [7] will become significant.2CH3.→C2H6  [7]
This probability is dictated by the thermodynamic “Equilibrium Constant of the reaction [7]”:
                              K          7                =                              [                                          C                2                            ⁢                              H                6                                      ]                                              [                                                CH                  3                                ⁢                •                            ]                        2                                              [                  Eq          .                                          ⁢          4                ]            where [CH3.] is the concentration of the Methyl radical and [C2H6] is the concentration of the Ethane.1.6.5—From Ethane to Propane
After a time period the gaseous mixture contains mainly molecular Methane, but also traces of the reactive Methyl radical and molecular Ethane. At a time Δt2 from the beginning of the process, where Δt2>>Δt1, the concentration of Ethane will reach a level where its presence affects the chemistry of the gas. The formation of the Ethyl radical may be predicted by the following reactions:Photolytic Initiation: C2H6+hv→C2H5.+H.  [8]Propagation: C2H6+CH3.→C2H5.+CH4  [9]
The Ethyl radical has a very short “life time” in a Methane saturated atmosphere. The reverse reaction of [9] is responsible for this short “life time”:C2H5.+CH4→C2H6+CH3.  [9]R 
Since the relative concentration of Methyl radicals is high, Propane may be formed by two different reactions:Termination: C2H5.+CH3.→C3H8  [10]Propagation: C2H6+CH3.→C3H8+H.  [11]
Reaction [11] has a low probability to occur because of steric hindrance reasons. But, since the concentration of methyl radical is big, it may occur.
1.6.6—From Propane to Higher Alkanes
For reactions of alkanes (having a generic formula CnH2n+2) in a rich Methane atmosphere, the general photolytic initiation reaction will be:CnH2n+2+hv→CnH2n+1.+H.  [12]
The Hydrogen radical will react as given in reaction [3] and it will follow the Hydrogen path explained in paragraph 1.6.2.
The Alkyl radical, CnH2n+1., will probably react with the surrounding Methane molecule to produce a Methyl radical:CnH2n+1.+CH4→CnH2n+2+CH3.  [13]
But also the substitution reaction (with low probability for steric reasons) may occur:CnH2n+1.+CH4→Cn+1H2n+4+H.  [14]
The termination reaction with the methyl radical is the main route for the formation of longer alkane molecules:CnH2n+1.+CH3.→Cn+1H2n+4  [15]
The experimental results show that the relative concentration of the produced alkenes will obey a Flory Distribution (Derk, 2008). This is in accordance with the chemical reactions sequence described in this last section.
1.6.7—Other Termination Reactions and Branched Isomer Formation
As the concentration of different alkyl radicals increases, the possibility of other termination reactions becomes significant. The general formulation of this possibility is:CnH2n+1.+Cn′H2n′+1.→Cn+n′H2(n+n′)+2  [16]
Steric hindrance gives preference to the formation of the linear isomer. But, with a lower probability, branched isomers are also formed by reaction [15] and [16]. Branching isomerization can be obtained also by the use of selective membranes or by radical internal reorganization.